The in vitro metabolism of radioactive androstenedione, pregnenolone and progesterone by rat placental homogenates has been studied. No estrogens were isolated but there was extensive ring A reduction of each compound. From the androstenedione incubations, 3α-hydroxy-5α-androstan-17-one, 3β-hydroxy- 5α-androstan-17-one, 5α-androstane-3α,17β-diol and 5α-androstane-3β,17β-diol were isolated by paper chromatography and identified by thin layer chromatography and the reverse isotope dilution technique. The metabolites of pregnenolone and progesterone were quantitatively and qualitatively similar. From these incubations 3α-hydroxy-5α-pregnan-20-one and 5α-pregnane-3α,20β-diol were isolated and identified. In the presence of a progesterone trap, progesterone- 7α-3H was found following the incubation of pregnenolone-7α-3H, demonstrating the presence of a 3β-ol-dehydrogenase Δ4–5-isomerase enzyme system. (Endocrinology87: 151, 1970) ATTEMPTS to evaluate possible endocrine functions of the rat placenta during pregnancy have been confined mainly to removal of the ovaries and/or gestational sacs under a variety of experimental conditions (1–6).
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Townsend et al. (1970) studied this question.